138 The Philippine Journal of Science ma 



Another set of experiments was carried on by using pure sap- 

 onin powder. A saturated solution of saponin in water was 

 made. One cubic centimeter of gold chloride was placed in a 

 test tube with saponin solution and boiled over a Bunsen burner. 

 By variations in the amount of gold and saponin present, and by 

 variations in the intensity of the heat applied, colors ranging 

 from dark blue to purplish red were obtained. All of these sus- 

 pensions settled out in from twenty-four to seventy-two hours. 

 It was noted that the colors always changed gradually, through 

 their various shades, to a dark blue, before settling. 



Another test was made by placing 1 cubic centimeter of gold 

 chloride solution in a beaker, adding 5 cubic centimeters of water, 

 and boiling. To the boiling solution was added about 0.1 gram of 

 saponin powder, which, upon further boiling, became a beautiful 

 clear red. This also, upon standing, changed through the various 

 purples to dark blue, and finally settled after seventy-two hours. 

 It was found that if the gold chloride solution contained excess 

 of acid, none of these reactions occurred. In such case sodium 

 carbonate had to be added to neutralize the acid. By adding 

 a few drops of sodium carbonate to 1 cubic centimeter of gold 

 chloride and then adding saponin powder or gogo, various shades 

 of red and purple were obtained which remained unchanged 

 upon standing. The reds were particularly clear and deep. The 

 application of heat seemed to be essential in all cases. 



Microscopic examination was made to determine whether or 

 not the solutions contained suspended metallic particles. By 

 concentrating the rays of a strong arc light upon a thin film of 

 solution placed upon a glass plate, the metallic particles could 

 easily be distinguished in all of these solutions. It was noted 

 that all of the purple and violet solutions had the same color by 

 reflected and transmitted light, but only a few of the red solutions 

 exhibited this characteristic; others, while showing beautiful 

 clear colors by transmitted light, gave a brownish, muddy color 

 by reflected light. 



It appears from these experiments that the red hydrosols rep- 

 resent the finest particles of gold, and the deep blue the largest 

 particles since the red changed to blue before complete precip- 

 itation. Whether this is due to a growth of the particle by 

 continued precipitation or the joining together of particles was 

 not determined. Furthermore, the finest particles would permit 

 the passage of longer wave lengths of light than the larger par- 

 ticles ; this would mean that the largest particles would transmit 



